EP2642165B1 - Hydrostatic drive - Google Patents

Description

The invention relates to a hydrostatic drive according to the preamble of patent claim 1.

Such hydrostatic drives are used for example in commercial vehicles as an auxiliary drive for an axle, for example, the front wheels, while the rear axle is driven by a conventional mechanical drive train.

Such a commercial vehicle with conventional and hydraulic drive train is for example in the DE 42 12 983 C2 explained. In this solution, the hydraulic drive train can be switched on if necessary via a valve arrangement, wherein each wheel of the front axle is associated with a hydraulic motor. The pressure medium supply takes place via a variable displacement pump. The known system is also designed with a retarder over which the brake system of the commercial vehicle is hydraulically assisted during braking.

In the EP 0 993 982 B1 is a vehicle with a conventional mechanical drive train and a generic hydrostatic drive explained. In this case, a hydraulic motor is assigned to both wheels of the front axle and executed in radial piston construction. Such a radial piston machine has a plurality of supported on a cam ring piston, each defining a working space, wherein the working spaces are connected in succession with high pressure and low pressure to drive the hydraulic motor. When switching off the hydraulic drive train this is adjusted to a "free-wheel mode" in which the working spaces with tank pressure or a comparatively low pressure are applied, while hubring- or housing side acts a feed pressure or other pressure greater than the tank pressure is. The resulting from the higher case pressure differential pressure causes a "retraction" of the piston so that they lift off from the cam and thus the friction is reduced with disconnected hydraulic drive train. When setting the pressure difference across the piston, make sure that the in Lifting effective pressure difference is so great that it holds the piston against the forces acting on the rotation forces in the Abhebestellung.

In the US 3,811,525 a hydrostatic drive is shown in which each wheel is assigned a hydraulic motor. These hydraulic motors can be switched over a valve assembly in the "free-wheel mode", in which case applied to the housing side of a feed pump applied feed pressure and in the work spaces of the tank pressure, so that the pistons to minimize friction from the cam ring stand out.

In the known solutions is also provided zuzuschalten the hydrostatic drive via a hydraulic clutch which connects in the "disengaged state" two connected to the terminals of the variable displacement working lines together (hydraulic bypass). Furthermore, a valve is provided, via which the housing is acted upon in the normal function with tank pressure, while in the above-described "free-wheel mode" the feed pressure is switched.

From the EP 0 309 222 A2 a hydrostatic drive is known, which has a fixed displacement pump and an adjustable hydraulic motor, which are operated together in a closed hydraulic circuit with a first circuit branch and with a second circuit branch, and a feed pump. Between the two circuit branches, an adjustable throttle valve is arranged, with which the transmitted from the pump to the hydraulic motor driving force can be controlled.

One problem is that the pressure medium at cold temperatures has a viscosity which is below a viscosity limit permitted for hydrostatic drives. It is therefore necessary to warm up the pressure medium before starting the vehicle in order to prevent damage to the hydrostatic drive.

From the generic US 4 951 466 A a hydrostatic drive is known which comprises an adjustable pump and a hydraulic motor, which are operated together in a closed hydraulic circuit with a first circuit branch and with a second circuit branch, and a feed pump. In a cold start mode, pressure fluid conveyed by the feed pump flows via a flow control valve and a viscosity-dependent throttle to a tank. In addition, in the cold start mode, the adjustable pump delivered from the feed pump pressure medium via a connected to a circuit branch pressure relief valve to the tank. The pressure set at the pressure relief valve is present at a connection of the hydraulic motor. In cold start mode, the adjustable pump is set to a small displacement volume.

In contrast, the invention has for its object to provide a hydrostatic drive, which is quickly ready for use even at cold temperatures.

This object is achieved by a hydrostatic drive having the features of patent claim 1.

Advantageous developments of the invention are the subject of the dependent claims.

According to the invention, the hydrostatic drive has a variable in its stroke pump and at least one hydraulic motor whose working connections in a closed hydraulic circuit via a first circuit branch and a second circuit branch, of which in a first operating mode high pressure and low pressure leads, connectable to working ports of the pump are. The hydrostatic drive further has a feed pump, from which via a feed line in which the pressure is limited to a low pressure, pressure medium can be fed into the circulation branches. There is a valve assembly available through the switching constellation different operating modes are adjustable. In addition, the hydrostatic drive also has an electronic control unit with which the switching constellations of the valve arrangement and possibly also the variable displacement pump are controlled. According to the invention, the electronic control unit is designed in such a way that in a cold start mode for heating pressure medium from the variable displacement pump, the pressure is fed to the other circuit branch from the variable pump fed by the feed pump, the valve arrangement being controlled in such a way that the pressure medium delivered by the variable displacement pump conveyed against a hydraulic resistance and guided, bypassing the hydraulic motor back to the tank.

The variable displacement pump is swung so far as it allows the current feed pressure maximum, so that a large amount is promoted. The funded by the feed pump and not removed by the variable amount is throttled back to the tank or on the suction side of the feed pump from the feed pressure to tank pressure and thus also heated. This heat input thus contributes to the heating of the pressure medium.

An inventive hydrostatic drive can, in addition to an active operating mode in which it is used as intended, also have a free-wheeling mode in which the hydraulic motor rotates freely. It is advantageous if in the free-wheeling mode, the feed pressure in the feed line is lower than in the active mode, since at low feed pressure, the energy losses are lower than at higher feed pressure. The lower feed pressure in free-wheel mode is also advantageous because the drive can be designed so that in this mode a housing connection, which has the motor housing of the hydraulic motor and which is open to the interior of the motor housing, flows from the supply line pressure medium to pressurize the interior of the motor housing with a low pressure and thereby lift the piston of the hydraulic motor from the lifting element. By the low supply pressure is the security high that the motor housing is not subjected inside to a high pressure.

Conveniently, the feed pressure in the cold start mode is lowered to the value in the free-wheeling mode. Thus, the switching constellation of the valve assembly in cold start mode compared to the free-wheeling mode is little to modify and the security is great that the motor housing is not subjected to an excessive internal pressure. For example, the feed pressure is lowered in the free-wheeling mode compared to the normal feed pressure of 20 to 30 bar in a range 8 to 10 bar. The feed pressure is usually available for adjusting the pump. At a lower feed pressure, the variable displacement pump is not adjustable to its maximum swing angle and swung out, for example, only 20%. For swinging out to 100%, the higher feed pressure would be necessary.

The drive is advantageously carried out with a so-called stand-by mode in which the valve assembly separates the working ports of the hydraulic motor of the tank and connects to the working ports of the pump and also connects the two working ports of the pump (10). In cold start mode, the valve assembly disconnects the two working ports of the pump in the cold start mode.

In a closed hydraulic circuit, the stroke volume of a feed pump designed as a fixed displacement pump is usually smaller than the maximum displacement of the adjustable main pump. For example, the stroke volume of the feed pump may be 28 cc and the maximum displacement of the variable displacement pump may be 140 cc, for example. Usually, the feed pump and the main pump are also driven at the same speed. Thus, even if you specify a maximum swing angle in the cold start mode for the variable, turns, whether the feed pressure is now deliberately lowered or not, a pivot angle of the variable, which is much smaller than the maximum swing angle. In fact, if the swivel angle of the variable displacement pump is so great that the variable displacement pump draws in more pressure medium than the feed pump, the charge pressure drops. However, this leads to a reduction of the swivel angle, since the drive uses a pump in particular is, in which for adjustment, the higher the pressure is necessary, the greater the swing angle. This is the case, for example, when the adjustment is made against a spring force. Because of the smaller swivel angle less pressure medium is sucked in by the pump. Finally, a stable state is established between the swivel angle and a feed pressure.

By using logic valves instead of complex special valves, the device construction of the circuit can be significantly reduced, the use of logic valves opens the possibility to implement additional variants with relatively little effort, so that the hydrostatic drive can be easily adapted to special requests of the customer can.

When hydrostatic drive can be arranged in each circuit branch Engage logic valve that opens the pressure medium connection between a working port of the pump and the corresponding working port of the hydraulic motor in an open position.

In a particularly preferred embodiment, both logic valves in the circulation branches together an Engage pilot valve is assigned, the pressure port with a feed pressure leading line and its output port to the pressure port or a tank port is connectable, the output port of Engage pilot valve with the spring chambers of Logic valves in the circulation branches and connected to a housing connection, which has the motor housing of the hydraulic motor and which is open to the interior of the motor housing.

For heating the pressure medium, the variable displacement pump then conveys against the Engage logic valve located in the high-pressure branch, which is acted upon by the feed pressure in the closing direction. That is, the Engage logic valve forms a hydraulic resistance, through which the heating of the pressure medium is accelerated.

This hydraulic resistance can be further increased when the engage logic valve is biased in the closing direction by the pump pressure. In this case The Engage logic valves would remain closed and one could propel against the high pressure valves in the pump (about 400 bar), which could significantly reduce the duration of the warm-up.

That is, the invention is not limited to forming the hydraulic resistance via the Engage logic valves, but other hydraulic components can be deliberately switched to generate a hydraulic resistance to quickly bring the pressure fluid to operating temperature.

In the feed pressure leading line, a flow control valve, in particular a nozzle may be provided, via which the pressure fluid flow is limited in the direction of the housing of the hydraulic motor. The flow control valve may also be a flow control valve.

In a further development of the invention, a relief logic valve, also referred to as unload logic valve, is connected between the logic valve in a circuit branch and the hydraulic motor to each circuit branch with a first connection, whose second connection is connected to the tank. By relieving the pressure of the pistons of a hydraulic motor to the tank, a free-wheeling operation mode can be realized, in which the pistons no longer abut on a lift curve. By a simultaneous pressurization of the piston from the interior of the housing ago, it will be ensured to an increased extent that the piston remain in a retracted position. Closing these unload logic valves will switch from a "free wheel mode" to a "standby" mode.

Via the unload logic valves, the heated pressure medium conveyed by the variable displacement pump can be led back to the tank.

To simplify the circuit complexity, both Unload logic valves are assigned a common unload pilot valve.

In one embodiment of the invention connects this Unload pilot valve in a basic position a spring chamber of the unloading logic valve with tank and in a switching position with the circuit branch, which carries the high pressure.

The high pressure can be tapped via a shuttle valve.

In one embodiment of the invention, the hydrostatic drive has a logic valve which connects the two circuit branches (or the pump connections) in the form of a bypass in an open position. This logic valve, which can also be referred to as a clutch logic valve, is assigned a clutch pilot valve via which a spring chamber of the clutch logic valve can be subjected to high pressure or relieved of pressure.

The hydrostatic drive can be designed to be particularly compact when the above-described logic valves and the associated pilot valves are combined to form a structural unit. In this unit can also be integrated for high pressure selection existing shuttle valve.

The hydrostatic drive has a feed pump, wherein in one embodiment, a filter is arranged in a feed line connected to the pressure port of the feed pump. This is associated with a pressure valve, which is acted upon by the pressure difference across the filter and its effective spring in the opening direction chamber via a feed pressure control valve to the tank is relieved. This pressure valve protects the filter from excessive pressures that could occur if the filter is dirty. Part of the oil pumped by the feed pump will be returned directly to the suction side of the feed pump. With a relief of the spring chamber, the pressure valve acts as a pressure relief valve. If the spring chamber of the pressure valve connected via a nozzle with a point downstream of the filter and used to relieve the spring chamber, a 2/2 way pilot valve, then flows when relief of the spring chamber, a control oil flow through the pilot valve. This control oil flow can be used to flush the pump housing.

According to the invention, a feed pressure limiting valve is arranged downstream of the filter, which opens at a higher pressure to the tank than the pressure valve on the filter with unloaded spring chamber. By the feed pressure relief valve, the amount of low pressure is determined during normal operation.

Such a circuit is known in the art, such as DE 10 2004 057 740 B4 known, so that further explanations are unnecessary.

In one embodiment of the invention, the hydrostatic drive is provided in a drive of a vehicle, wherein each wheel of an axle is provided with a hydraulic motor. The other axle is preferably driven in a conventional manner via a mechanical gear.

The pivoting direction of the variable during cold start preferably corresponds to the pivoting direction when driving forward.

A preferred embodiment of the invention will be explained in more detail below with reference to drawings.

• Figur 1 einen Schaltplan eines erfindungsgemäßen hydrostatischen Antriebs einer Fahrzeugachse,
• Figur 2 eine vergrößerte Darstellung der Pumpeneinheit gemäß Figur 1,
• Figur 3 eine vergrößerte Darstellung eines Ventilblocks gemäß Figur 1 und
• Figur 4 eine vergrößerte Darstellung einer Hydromotoreinheit gemäß Figur 1.

Show it:

• FIG. 1 a circuit diagram of a hydrostatic drive according to the invention a vehicle axle,
• FIG. 2 an enlarged view of the pump unit according to FIG. 1 .
• FIG. 3 an enlarged view of a valve block according to FIG. 1 and
• FIG. 4 an enlarged view of a hydraulic motor unit according to FIG. 1 ,

The hydrostatic drive according to the invention can be used for example in a truck whose rear wheels are driven by a conventional mechanical drive train with internal combustion engine, transmission, propeller shaft and differential. In addition, a hydrostatic drive is provided, which can be switched on, for example, in heavy terrain. According to the in FIG. 1 the circuit diagram shown, the hydrostatic drive 1 has a pump unit 2, which is driven by the internal combustion engine. This pump unit 2 supplies, via a valve arrangement, referred to below as valve block 4, two hydraulic motor units 6a, 6b via which a respective front wheel 8a, 8b is driven. The in FIG. 1 shown hydrostatic drive 1 is designed as a closed circuit. The aforementioned Components of the hydrostatic drive 1 are based on the FIGS. 2 to 4 explained in more detail.

FIG. 2 shows an enlarged view of the pump unit 2 from FIG. 1 ,

The pump unit 2 has a via a zero position (briefly: above zero) pivotable variable 10, which is driven by the internal combustion engine and a maximum displacement (flow rate per revolution) of, for example 140 cc has. Pivoting about a zero position means that, as in the present case, the direction of the pressure medium flow by a hydraulic unit in a pump or motor mode while maintaining the direction of rotation of a drive shaft and changing from high pressure and low pressure connection reverses or that while maintaining high pressure and Low pressure connection and while maintaining the direction of rotation of a drive shaft, a change between pump operation and engine operation takes place. The drive takes place via a drive shaft 12, which also drives a feed pump 14 designed as a fixed displacement pump with a displacement of, for example, 28 cc. About this pressure medium from a tank T (see also FIG. 1 ) sucked and fed with a feed pressure of for example 20 to 30 bar in a low-pressure branch of the hydrostatic drive 1. The following explanations assume that an in FIG. 2 overhead pressure line is a low pressure line 16, while a connected to the other terminal of the variable displacement 10 pressure line to be the high pressure line 18. Depending on the direction of the variable displacement pump 10, however, the high-pressure branch and the low-pressure branch can change.

The adjustment of the pivot angle of the variable displacement pump 10 by means of a control cylinder 20 which is controlled by a pump control valve 22 which is designed as controlled via a control electronics proportional valve. Such pressure and flow control valves for variable displacement pumps are known from the prior art, so that can be dispensed with a detailed explanation. The pump control valve 22 is set as a set value as electrical variable and adjusted in response to the control of the pump control valve 22, a control piston of the actuating cylinder 42, wherein this is carried out with a mechanical or electrical feedback. The position of the actuating piston is mechanically or via the control electronics with compared to the predetermined target value, which corresponds to a certain displacement and the actuator piston is adjusted so long until the setpoint and actual value match and thus adjusted in consideration of the speed of the required flow rate. According to the assumed conveying direction of the variable displacement pump 10, the pressure medium is conveyed into the high pressure line 18 and flows back to the load, in the present case to the hydraulic motor units 6a, 6b and in a closed circuit via the low pressure line 16 to the low pressure connection of the variable displacement 10. For further details of such a pump control is for example on the DE 10 2004 061 861 B4 directed.

The pump unit 2 further has two feed valves 24, 26, can be fed via the pressure medium in the respective low-pressure branch. Each of these feed valves 24, 26 has in known manner in each case one to a line 16, 18 toward opening check valve 28 to which a pressure relief valve 30 is connected in parallel, which when exceeding a predetermined pressure in the associated pressure line (here 18) a pressure medium connection to each other pressure line (here 16) aufsteuert. With regard to the concrete structure of such feed valves 24, 26 can also on the DE 10 2004 061 861 B4 to get expelled.

The two input terminals of the feed valves 24, 26 are connected to a feed passage 32 which is connected to a filter unit 34, whose input port is connected to the pressure port of the feed pump 14. A suction port of the feed pump 14 is connected to the tank T via a tank port T and a suction line 36. Via the feed pump 14, pressure medium is supplied with the feed pressure (20 to 30 bar) and conveyed via the filter unit 34 and the feed channel 32 to the inlet of the two feed valves 24, 26. The low-pressure side check valve 28 then opens, so that pressure medium is conveyed into the corresponding low-pressure branch. The pressure in the high-pressure branch is limited by the respective pressure-limiting valve 30 of the feed valve 24, 26, so that when this maximum pressure is exceeded, the pressure can be reduced to the low-pressure side.

As shown in FIG. 2 the filter unit 34 is designed with a pressure valve 38, the pressure upstream of a filter 40 in the opening direction and of Pressure downstream of the filter 40 is acted upon in the closing direction. In the closing direction also acts a spring. As the contamination increases, the pressure drop across the filter 40 increases. At a certain pressure drop, the pressure valve 38 starts to open a bypass line 42 to the suction line 36, so that the filter is protected from excessive pressures. The effective pressure in the closing direction downstream of the filter 40 is tapped via a control channel 44 in which a feed pressure control valve 46 is arranged, which is biased by a spring into a closed position and can be brought via a solenoid in an open position in which the control channel 44 via the Pump housing is relieved to the tank T out. As in the illustration according to the FIGS. 1 and 2 indicated, the output of the feed pressure control valve 46 is connected to a leakage line 64 which is connected via the pump housing of the variable displacement pump 10 to the tank T. The connection to the pump housing is in FIG. 2 marked with the terminals T1, T2. By switching the feed pressure control valve 46 in its open position, the effective in the closing direction control surface of the pressure valve 38 can be relieved, so that it acts as a pressure relief valve, which limits the pressure upstream of the filter 40. Downstream of the filter 40, a feed pressure limiting valve 48 is provided in the feed passage 32, which opens according to the invention at a higher pressure (for example 20 to 30 bar) than the differential pressure valve 38 in the above-described pressure limiting function. This opens then, for example, when switching the feed pressure control valve, the pressure medium connection to the tank T at a pressure which is below the pressure of the feed pressure relief valve 48, for example, at about 5 to 7 bar. The feed pressure is then reduced accordingly. The mode of operation and the concrete structure of such a filter unit 34 with two pressure relief valves set to different values is described, for example, in US Pat DE 10 2004 057 740 B4 explained.

The pump unit further has a Druckabschneideventileinheit 50, via which the pressure in the high-pressure branch tapped by means of a shuttle valve 52 and into a control chamber of a Druckabschneideventils 54 which throttles when a predetermined maximum pressure exceeds a control line 56 connected to tank, so that the variable displacement pump 10 in Direction of a lower flow rate is adjusted. For further details of such Druckabschneideventileinheit 50 can also on the DE 10 2004 061 861 B4 to get expelled.

The pump unit 16 has two working ports A, B, which are connected via working lines 58, 60 with the valve block 4, which will be explained in greater detail below. The pump unit 16 further has a feed connection G, which is connected via an internal channel to the feed channel 32 and to which a feed line 62 is connected. The suction line 36 is connected via a tank connection T with the tank T. A connected to the output of the feed pressure control valve 46 leakage line 64 is connected via an in FIG. 1 shown cooling / filter unit 66 connected to the tank T, so that withdrawn from the closed circuit pressure fluid is cooled and filtered and then back through the feed pump 14 can be promoted back into the closed circuit.

FIG. 3 shows the valve block according to FIG. 1 in an enlarged view. This is composed in principle of three valve devices, which are referred to below as a clutch valve device 68, as Engage valve device 70 and as Unload valve device 72. According to the invention, these valve devices are in principle formed by interconnected pilot-operated logic valves, by means of which the functions of the special valves described in the introduction are realized in the prior art.

As shown in FIG. 3 the valve block has ports A, B, G and T1, which are connected to the respective ports of the pump unit 2. To the two working ports A, B, the above-described working lines 58, 60 are connected, while the feed port G is in fluid communication with the feed line 62. The leakage port T1 is connected to a leakage or return passage 74.

The clutch valve device 68 has a clutch logic valve 76 whose port A is connected to the working line 58 and whose other port B is connected to the other working line 60. The clutch logic valve 76 is associated with a clutch pilot valve 78, via which a spring chamber 80 of the clutch pilot valve 76, hereinafter called C pilot valve, in a spring-loaded basic position with the return passage 74 and in an occupied when driving a pulling solenoid Switching position with the high-pressure branch is connectable, so that then the high pressure in the spring chamber 80 is effective. The high pressure is tapped via a shuttle valve 120 from the working channels 58, 60. The output of the C pilot valve 78 is connected to the spring chamber 80 via a connection plate 82 of the C logic valve 76.

In the illustrated basic position thus acts in the spring chamber 80 of the tank pressure, so that the C-logic valve 76 is brought by the pressure in the working lines 58, 60, in particular by the effective according to the specifications in the working line 60 high pressure in an open position and the two Pump connections connecting working lines 58, 60 are short-circuited via the C-logic valve 76. The pressure medium supply to the hydraulic motors is thus interrupted.

Engage valve assembly 70 has two engagement logic valves 84, 86, hereafter e-logic valves 84, 86. The radial ports of the e-logic valves 84, 86 are connected to the working line 58 and 60, respectively. The two other ports of the two logic E-valves 84, 86 open into a working channel 88 and 90. Both Engage logic valves 84, 86 is associated with an E-pilot valve 92, which is designed in the illustrated embodiment as a 4/2-way valve and over a spring is biased in an open position, in which spring chambers 94, 96 of the e-logic valves 84 and 86 are connected to the feed line 62, so that acts in the spring chambers 94, 96 of the feed pressure. By switching the E-pilot valve 92, the spring chambers 94, 96 are connected to the return passage 74 and thus relieved of pressure. The output terminal of the E pilot valve 92 is connected via a control channel 98 and connection plates 100, 102 with the respective spring chamber 94 and 96, respectively. From the control channel 98 branches off a channel 1004, which with a housing connection G of the hydraulic motor units 6a, 6b, (see FIG. 4 ) connected is.

Depending on the switching position of the E pilot valve 92, the channel 104 is thus connected to the feed line 62 or to the return line 74, in which tank pressure prevails.

In the area between the port G of the valve block and the E-pilot valve 92, a nozzle 108 is provided, via which in the illustrated basic position of the E-pilot valve 92 of the pressure medium volume flow to the housing of the hydraulic motor units 6a, 6b is limited.

In illustration according to FIG. 3 the E-pilot valve unit 92 is in its home position, which it is connected in the "free-wheel mode" and in the channel 104 to the feed line 62. The two e-logic valves 84, 86 are held in their closed position by the current supply pressure acting on the large rearward control surface and, since the clutch logic valve 76 is open, the smaller, front annular surface of the respective logic valve 84, 86. so that the pressure medium connection from the working channel 88 to the working line 58 and from the working channel 90 to the working line 60 is interrupted. The central front control surface of the logic valve 84, 86 is relieved in free wheeling mode to the tank, as will emerge from the further description.

The unload valve device 72 has two pilot-operated unload logic valves 110, 112 (U logic valve) whose axial ports are connected to the working channels 88 and 90, respectively, and whose radial output ports are connected to the return port 74. Both U logic valves 110, 112 together have an unloading pilot valve 114 assigned to it, which in the exemplary embodiment shown is designed as a 3/2-way valve and in its spring-biased basic position connects the two spring chambers 116, 118 with the return channel 74. By switching the U-pilot valve 114, the spring chambers 116, 118 are acted upon by the pressure in the high-pressure branch, which is tapped via the shuttle valve 120 to the working lines 58, 60. The output of this shuttle valve 120 is connected via an HD control line 121 to the input of the U pilot valve 114.

In the illustrated "free wheel mode", the spring chambers 116, 118 in the basic position of the U pilot valve 114 are connected to the return passage 74 and thus depressurized. The U logic valves 110, 112 can therefore be controlled by the effective pressure in the opening direction, so that the two working channels 88, 90 are connected to the tank and thus in the working spaces of the hydraulic motors corresponding tank pressure acts, while the housing side, the feed pressure is effective and thus Lift the pistons off the cam ring. The tank pressure in the working channels 88 and 90 is also at the central, front control surfaces of the e-logic valves 84, 86 at.

As previously discussed, C-logic valve 76 bypasses between working lines 58, 60. This C-logic valve 76 is kept open until sufficient synchronization of the conventionally driven rear wheels and front wheels is ensured to avoid unexpected pressure spikes. After closing the C logic valve 76, the short circuit between the working lines 58, 60 is released, so that a torque is applied to the hydraulic motors. At the measuring point MT, a temperature sensor 124 is arranged, which detects the temperature of the pressure medium in the return passage 74.

Via the E-valve device 70, the connection of the working lines 58, 60 is controlled to the hydraulic motor units 6a, 6b. In addition, the E-valve device 70 controls the "free-wheel mode" in which the pistons of the hydraulic motors, as explained above, lift off from the cam ring.

Via the U-valve device 72, the pressure medium connection of the hydraulic motors is controlled to the tank. The pressures in the working channels 88, 90 can be detected by pressure sensors 122, of which FIG. 1 two and in the illustration according to FIG. 3 only one example is shown.

The pressure medium supply of the hydraulic motor units 6a, 6b takes place via the working connections A ', B' and the connection G ', of the valve block 4.

The function of the hydraulic motor units 6a, 6b is exemplified by means of FIG. 4 explains that the hydraulic motor unit 6b from FIG. 1 shows.

The hydraulic motor unit 6a has a hydraulic motor 130, which is designed as a non-adjustable hydraulic machine.

As explained, the hydraulic motor is designed, for example, as a radial piston machine, with a radial piston engine, wherein a plurality of pistons on an outside lying lifting ring are supported. The radial piston machine can also be designed with an inner cam ring. Since the construction of such radial piston machines is well known, can be dispensed with further explanation with reference to the prior art. The above-described working ports A ', B' are connected via connecting lines 132, 134 to the corresponding ports A, B of the hydraulic motor unit 6b. This also has a housing connection G, which is connected via a line 136 to the terminal G 'of the valve block 4. As already explained above, a channel 138 is connected to the housing connection G, which opens into the interior of the motor housing. That is, the pistons of the radial piston engine are acted upon by the pressure in the channel 138 in the direction of lifting from the lifting ring, as in the FIGS. 1 and 4 is indicated. Depending on the switching position of the Engage pilot valve 92, this pressure may correspond to the tank pressure or an increased pressure. The two ports of the hydraulic motor 130 are connected via a working channel 140, 142 with the terminals A, B.

From channel 138, a freewheel channel 144 branches off, which connects the housing interior with the working channel 142. In the freewheel channel 144, a spring-biased check valve 146 is provided, whose spring corresponds to a pressure equivalent of, for example, 3 bar and which opens to the working channel 142. To open this check valve 146, the pressure acting upstream of the check valve must be about 3 bar higher than the pressure acting on the back of the check valve 146. The check valve 146 thus ensures that the pressure in the housing interior does not fall below 3 bar. With this pressure, the pistons are acted upon in the direction of retraction into the cylinders in free-wheeling mode.

Of the two working channels 140, 142 each have a channel 148, 150 branches off, which are guided to two input ports of a purge valve 152.

This is designed as a 3/3-way valve and has an output terminal C, to which a connecting channel 154 is connected, which opens upstream of the check valve 146 in the Freewheelkanal 144.

The purge valve 152 has a spring-centered position in which the three ports are shut off from each other. The pressure in the channels 148, 150 is tapped in each case via control channels 156, 158 and guided to two opposing control surfaces of the purge valve, so that the purge valve is adjusted by the effective in the working channels 140, 142 pressure difference in the direction of a switching position a or b. In the connecting channel 154, a throttle 160 is arranged. Downstream of this throttle 160, a pressure-holding valve 162 is provided, which is biased by a spring into a blocking position and which is acted upon by the pressure upstream of the throttle 160 in the direction of an open position.

This pressure-holding valve 162 opens only when the pressure in the connecting channel 154 and thus the lower pressure from the two working channels 140, 142 has exceeded a threshold corresponding to the spring of the pressure-maintaining valve 162. The basic structure of such a purge valve is in the EP 1 443 220 B1 explained, in this variant, a pressure shut-off valve is still provided.

In a cold start of the hydrostatic drive for heating the pressure medium, the variable displacement pump 10, the pivot angle is set via the control unit 23, for example, to the maximum setpoint. Since the displacement of the feed pump is substantially smaller than the maximum displacement of the variable 10, it turns, as already stated above, by itself a pivot angle of the variable, which is much smaller than the maximum Schenk angle. A deliberate reduction of the feed pressure as in free-wheeling mode is then largely without practical effect, since the feed pressure would drop anyway because of the difference between the displacement of the feed pump 14 and the maximum displacement of the variable. Of course, the intentionally set lower feed pressure must still be high enough to be able to adjust the pump. The deliberate lowering brings with it that some valves can be controlled in the same way in cold start mode and in free-wheeling mode. The conscious lowering of the feed pressure also increases the certainty that the inside of the motor housing is not subjected to too high a pressure.

At the same time, the clutch logic valve 76 is biased toward its closed position for heating, so that the bypass between the working lines 58, 60 is closed. For this purpose, the C-pilot valve 78 is switched from its basic position, so that in the spring chamber 80 of the tapped via the shuttle valve 120 high pressure is applied.

The two e-logic valves 84, 86 are when heated in the in FIG. 3 represented position via the E-pilot valve 92 in the direction of its closed position with a pressure which adjusts downstream of the nozzle 108. Upstream of the nozzle 108 is the lower feed pressure. This is set via the pressure valve 38 and the feed pressure control valve 46 to a lower value (for example 8 to 10 bar) or lower due to the behavior of the variable than it is in normal operation (20 to 30 bar feed pressure). To the conscious reduction of the feed pressure, the feed pressure control valve 46 is switched to its open position, so that the pressure valve 38 is depressurized in the closing direction and thus limits the feed pressure to the pressure equivalent of its spring corresponding value, wherein a control oil flow through the open feed pressure control valve 46, the leakage line 64th and the housing of the pump 10 flows toward the tank T out and is also heated. The pressure after the nozzle 108 then acts on the E-logic valves 84, 86 in the closing direction, while on the annular surface of the one E-logic valve, the high pressure and the annular surface of the other E-logic valve, the low pressure (feed pressure) acts. The variable displacement pump thus promotes against the high pressure side arranged, biased in the closing direction E-logic valve 84 or 86 (depending on the conveying direction), which allows a flow of pressure medium in the direction of the two U-logic valves 110, 112. These are also in the in FIG. 3 shown biased position, wherein the U-pilot valve 114 is in its illustrated basic position in which the spring chambers 116, 118 are relieved of pressure to the tank. The located in the high-pressure branch U-logic valve 110, 116 is controlled by acting on its end face pressure, according to the low-pressure side U-logic valve in the opening direction of the low pressure (feed pressure) is applied, so that the pressure medium via the respective U-logic valve 110, 112 for Tank T can flow out. Between the on
controlled E-logic valve 84 or 86 and the corresponding U-logic valve thereby builds up a pressure which is necessary to open the U-logic valve by pressurizing the central, front end face against the spring. This pressure also acts on the central face of the opened e-logic valve. At the radial port of this e-logic valve, a pressure is set, which is so great that the pressure force generated by him at the annular surface of the E-logic valve together with the pressure force generated at the central front end face the E-logic valve against the spring force and the held by the feed pressure at the rear end face pressure force open. Due to the comparatively high hydraulic resistance of the high-pressure branch located in the E-logic valve 84 and 86, the pressure medium is heated very quickly and brought into the desired viscosity range.

The nozzle 108 has primarily the function to limit the inflow of pressure medium into the motor housing. It could therefore also be arranged in the line 104. Then the E-valves would be applied in the cold start mode with the reduced feed pressure in the closing direction. It would be a higher high pressure set, because the reduced feed pressure is higher than the pressure downstream of the nozzle 108. A nozzle in the conduit 104 could be connected in parallel with a check valve opening towards the valve 92 in order to allow a large amount of oil to flow off quickly after switching over of the valve 92.

As explained above, the heating can be accelerated by the two E-logic valves 84, 86 are acted upon by the high pressure in the closing direction.

In summary, one can note:

In the cold start mode, the oil flow is heated, which flows via the feed pump 14, via the filter 40, via the variable displacement pump 10 and via an E-logic valve and a U-logic valve to the tank. It also heats the flow of oil flowing through the feed pump 14, through the filter 40, the nozzle between the outlet of the filter 40 and the spring chamber of the valve 38 and the valve 46 to the tank. It is, if oil flows here, also an oil flow heated via the feed pump 14, via the filter 40, via the nozzle 108, via the valve 92 and the housing of the hydraulic motors 6a, 6b, via the Check valves 146, via a working port of a hydraulic motor and a U-logic valve flows to the tank.
Is the predetermined by the valve 38 with relieved spring chamber, maximum lowered feed pressure not so large that the variable displacement pump 10 can swing so far that this can promote the whole of the feed pumped amount, so flows through the valve 38, a residual amount back to Also, this amount is heated and mixed with the other, sucked by the feed pump from the tank amount of oil, so that an oil flow through the valve 38 contributes to the heat input into the total amount of oil.

As explained, in the in FIG. 1 shown basic position of the valve block 4 of the "free-wheel mode" set. That is, via the C-valve means 68, the working lines 58, 60 are short-circuited. The E-pilot valve 92 switches the feed pressure in the housing of the hydraulic motor 130 by. The working spaces of the hydraulic motor are connected via the U-valve device 72 to the tank. The pistons of the hydraulic motor 130 are thus acted upon in the sense of lifting by the lifting ring. The accumulator pressure control valve 46 is switched to its open position, so that the feed pressure is reduced to the value set at the pressure valve 38.

As explained, the two working channels 140, 142 are relieved towards the tank T, so that the tank pressure is applied to the rear side of the check valve 146. The pressure upstream of the check valve is accordingly limited to 3 bar or more precisely the pressure equivalent of the spring of the check valve 146 corresponding pressure. This pressure is sufficient to keep the pistons of the hydraulic motor 130 against centrifugal force in their retracted position. In this "free-wheel mode", the drive shaft 12 is driven, so that accordingly the feed pressure is available. The variable displacement pump 10 can be moved back.

When the hydrostatic drive is switched on, the e-pilot valve 92 is initially switched so that the tank pressure is effective on the housing side and the pistons can rest against the cam ring. The e-logic valves 84, 86 open by the discharge in the spring chamber 94, 96 and due to the effective pressure in the opening direction. The ports A, B of the pump unit 2 are still over shorted the C-logic valve device. In a corresponding manner, the connections A, B of the hydraulic motor units 6a, 6b are connected to the tank via the U-valve device 72.

In a following sequence, the swivel angle of the variable displacement pump 10 is then adjusted so that the flow rate of the pump corresponds to the displacement volume flow of the two hydraulic motor units 6a, 6b plus a predetermined displacement volumetric flow difference. As a result, the U pilot valve 114 is then switched so that the ports A, B, the hydraulic motor units 6a, 6b are connected to the working channels 88, 90 and thus the hydraulic motors are connected to the hydraulic network of the pump. The final connection is then made by switching the C-valve device 68 in its blocking position.

The shutdown of the hydrostatic drive then takes place in a corresponding manner.

Disclosed is a hydrostatic drive with a closed circuit, wherein at least one hydraulic motor is supplied via a variable displacement pump with pressure medium. The drive has a feed pump, wherein for the heating of the pressure medium, the variable displacement pump is supplied by the feed pump with pressure medium and this promotes against a predetermined hydraulic resistance to the tank.

Claims (16)

1. Hydrostatic drive having a pump (10) with an adjustable swept volume, having at least one hydraulic motor (6a, 6b), the operating connectors of which can be connected to operating connectors of the pump (10) in a closed hydraulic circuit via a first circuit branch and a second circuit branch, of which one conducts high pressure and one conducts low pressure in a first operating mode, having a feed pump (14), by which pressure medium can be fed into the circuit branches via a feed line, in which the pressure is limited to a low pressure, having a valve arrangement (4), by way of the switching configuration of which different operating modes can be set, and having an electronic control unit (23), characterized in that the electronic control unit (23) is designed in such a way that pressure medium is conveyed by the variable displacement pump (10) from the one circuit branch which is fed by the feed pump (14) into the other circuit branch in a cold starting mode in order to heat pressure medium, the variable displacement pump (10) being swung out as far as the current feed pressure allows, and the valve arrangement (4) being actuated in such a way that the pressure medium which is conveyed by the variable displacement pump (10) is conveyed counter to a hydraulic resistance and is conducted back to the tank while bypassing the hydraulic motor (130).
2. Hydrostatic drive according to Patent Claim 1, the valve arrangement (4), in one operating mode (freewheeling mode), disconnecting the operating connectors of the pump (10) and the hydraulic motor (6a, 6b) from one another, connecting the operating connectors of the pump (10) to one another, and connecting the operating connectors of the hydraulic motor (6a, 6b) to a tank, and, in the said operating mode, pressure medium flowing out of the feed line to a housing connector which the motor housing of the hydraulic motor (6a, 6b) has and which is open towards the interior space of the motor housing, in order to load the interior space of the motor housing with a low pressure, the valve arrangement (4), in a further operating mode (active mode), disconnecting the two operating connectors of the pump (10) from one another and disconnecting the two operating connectors of the hydraulic motor (6a, 6b) from the tank, and connecting the one operating connector of the pump (10) to the one operating connector of the hydraulic motor (6a, 6b) and connecting the other operating connector of the pump (10) to the other operating connector of the hydraulic motor (6a, 6b), and the feed pressure in the feed line being limited to a lower value in the cold starting mode and in the freewheeling mode than in the active mode.
3. Hydrostatic drive according to Patent Claim 2, pressure medium flowing into the interior space of the motor housing in the freewheeling mode via a flow control valve, in particular via a nozzle (108), and a check valve (146) which opens towards the operating connector being arranged between the interior space and an operating connector of the hydraulic motor (6a, 6b).
4. Hydrostatic drive according to Patent Claim 2 or 3, the valve arrangement (4), in another operating mode (standby mode), disconnecting the operating connectors of the hydraulic motor from the tank and connecting them to the operating connectors of the pump (10) and, moreover, connecting the two operating connectors of the pump (10) to one another, and the valve arrangement (4) disconnecting the two operating connectors of the pump (10) from one another in the cold starting mode.
5. Hydrostatic drive according to one of Patent Claims 1 to 4, a two-way cartridge valve (logic valve) (84, 86) being arranged in each circuit branch, which two-way cartridge valve (84, 86) opens the pressure medium connection between an operating connector of the pump (10) and the corresponding operating connector of the hydraulic motor (130) in an open position, the two logic valves (84, 86) in the circuit branches being jointly assigned an engage pilot control valve (92), the pressure connector of which can be connected to a line which conducts the feed pressure, and the outlet connector of which can be connected to the pressure connector or a tank connector, the outlet connector of the engage pilot control valve (92) being connected to the spring spaces (94, 96) of the logic valves (84, 86) in the circuit branches and to a housing connector which the motor housing of the hydraulic motor (6a, 6b) has and which is open towards the interior space of the motor housing.
6. Hydrostatic drive according to Patent Claim 5, a flow control valve, in particular a nozzle (108), being arranged in the line which conducts the feed pressure flows in, and a check valve (146) which opens towards the operating connector being arranged between the interior space of the motor housing and an operating connector of the hydraulic motor (6a, 6b).
7. Hydrostatic drive according to a preceding patent claim, a relief logic valve (unload logic valve) (110, 112) being connected by way of a first connector to each circuit branch between the logic valve (84, 86) in a circuit branch and the hydraulic motor (6a, 6b), the second connector of which relief logic valve (110, 112) is connected to the tank, it being possible for the two relief logic valves (110, 112) to be actuated via a common unload pilot control valve (114).
8. Hydrostatic drive according to Patent Claim 7, the unload pilot control valve (114) loading a spring space (116, 118) of the relief logic valves (110, 112) to tank pressure in a basic position and loading it with high pressure in a switched position.
9. Hydrostatic drive according to Patent Claim 8, there being a shuttle valve (120), via which a pilot control valve (78, 114) is connected to the circuit branch which conducts the high pressure.
10. Hydrostatic drive according to a preceding patent claim, a filter (40) being arranged in the feed line (32) which is connected to the pressure connector of the feed pump (14), which filter (40) is assigned a pressure valve (38) which is loaded by the pressure difference across the filter (40), and the spring space of which, which acts in the opening direction, can be relieved to the tank via a feed pressure control valve (46), and a feed pressure limiting valve (48) being arranged downstream of the filter (40), which feed pressure limiting valve (48) opens to the tank at a higher pressure than the pressure valve (38) in the case of a relieved spring space.
11. Hydrostatic drive according to a preceding patent claim, a logic valve (76) connecting the two circuit branches to one another on the pump side in an open position, it being possible for a spring space (80) of the logic valve (76) to be loaded with high pressure and to be relieved of pressure via a clutch pilot control valve (78) depending on its switched position.
12. Hydrostatic drive according to a preceding patent claim, the logic valves (76, 84, 86, 110, 116) and the associated pilot control valves (78, 92, 114) being combined to form one structural unit.
13. Hydrostatic drive according to a preceding patent claim, the said hydrostatic drive being a traction drive for a vehicle axle, in which each wheel (8) is assigned one hydraulic motor.
14. Hydrostatic drive according to Patent Claim 12, having a conventional drive for the other axle.
15. Hydrostatic drive according to Patent Claim 12 or 13, the variable displacement pump (10) being set in the cold starting mode in a delivery direction which corresponds to forward driving.
16. Hydrostatic drive according to a preceding patent claim, the swept volume of the feed pump (14) being smaller than the maximum swept volume of the adjustable pump (10).

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